TAMPA — A federal judge ruled Friday that the pill John Andrew Welden tricked his girlfriend into taking did cause the death of her six-week-old embryo.

The decision by U.S. District Judge Richard A. Lazzara, reached after two days of testimony from dueling experts, leaves in place a deal in which Welden pleaded guilty to product tampering, and both sides recommended a sentence of 13 years and eight months in prison.

Lazzara not rule yet on the ultimate sentence, however, finding however that the sentencing guidelines give a range of 135 to 168 months. He did not decide whether to impose the 164-month sentence recommended by the parties. He scheduled sentencing for Jan. 27.

In agreeing to the plea deal, Welden avoided a potential sentence of life without parole. He admitted that he forged a prescription from his OB-GYN father and tricked his pregnant girlfriend, Remee Lee, into taking the pill by disguising it as an antibiotic.

The prosecution said Welden wanted to keep his other girlfriend from learning of the pregnancy.

The defense argued that the evidence didn’t support that the single, 200-microgram dose of Cytotec, also known as Misoprostol, caused the embryo to abort. Rather, they presented expert testimony that it was impossible to prove what caused the miscarriage.

Defense experts also said it was possible Lee was losing the baby before she took the pill, something Lazzara outright rejected, noting Lee had an ultrasound two days before and the pregnancy was found to be viable.

“The suggestion that prior to the ingestion of this highly toxic drug, this victim was experiencing a spontaneous abortion is just speculation not supported by the record,” the judge said. “The only rational explanation for what caused the demise of the victim’s embryo was her ingestion of one dose of 200 micrograms of Misoprostol.”

Lazzara gave more credence to prosecution experts, who he said had more direct experience with patients and with the drug itself.

The judge said defense experts merely served as conduits for information they found in scientific literature, which the judge said amounted to no more than case studies with little supporting information. This, he said, was “useless to me in determining a relationship of Misoprostol to a particular side effect.”